[dpdk-dev] [PATCH v2 01/12] eal: define container_of macro

[Adrien Mazarguil]

On Fri, Dec 16, 2016 at 09:14:29AM +0100, Jan Blunck wrote:
> On Wed, Dec 14, 2016 at 6:12 AM, Shreyansh Jain <shreyansh.jain at nxp.com> wrote:
> > On Wednesday 14 December 2016 03:54 AM, Jan Blunck wrote:
> >>
> >> On Tue, Dec 13, 2016 at 2:37 PM, Shreyansh Jain <shreyansh.jain at nxp.com>
> >> wrote:
> >>>
> >>> From: Jan Blunck <jblunck at infradead.org>
> >>>
> >>> This macro is based on Jan Viktorin's original patch but also checks the
> >>> type of the passed pointer against the type of the member.
> >>>
> >>> Signed-off-by: Jan Viktorin <viktorin at rehivetech.com>
> >>> [shreyansh.jain at nxp.com: Fix checkpatch error]
> >>> Signed-off-by: Shreyansh Jain <shreyansh.jain at nxp.com>
> >>> [jblunck at infradead.org: add type checking and __extension__]
> >>> Signed-off-by: Jan Blunck <jblunck at infradead.org>
> >>>
> >>> --
> >>> v2:
> >>>  - fix checkpatch error
> >>> ---
> >>>  lib/librte_eal/common/include/rte_common.h | 21 +++++++++++++++++++++
> >>>  1 file changed, 21 insertions(+)
> >>>
> >>> diff --git a/lib/librte_eal/common/include/rte_common.h
> >>> b/lib/librte_eal/common/include/rte_common.h
> >>> index db5ac91..3eb8d11 100644
> >>> --- a/lib/librte_eal/common/include/rte_common.h
> >>> +++ b/lib/librte_eal/common/include/rte_common.h
> >>> @@ -331,6 +331,27 @@ rte_bsf32(uint32_t v)
> >>>  #define offsetof(TYPE, MEMBER)  __builtin_offsetof (TYPE, MEMBER)
> >>>  #endif
> >>>
> >>> +/**
> >>> + * Return pointer to the wrapping struct instance.
> >>> + *
> >>> + * Example:
> >>> + *
> >>> + *  struct wrapper {
> >>> + *      ...
> >>> + *      struct child c;
> >>> + *      ...
> >>> + *  };
> >>> + *
> >>> + *  struct child *x = obtain(...);
> >>> + *  struct wrapper *w = container_of(x, struct wrapper, c);
> >>> + */
> >>> +#ifndef container_of
> >>> +#define container_of(ptr, type, member)        (__extension__  ({
> >>> \
> >>> +                       typeof(((type *)0)->member) * _ptr = (ptr);     \
> >>> +                       (type *)(((char *)_ptr) - offsetof(type,
> >>> member));\
> >>> +                       }))
> >>
> >>
> >> This is a checkpatch false positive. It should be fine to ignore this.
> >> IIRC we already discussed this before.
> >
> >
> > I too thought something similar was discussed. I tried searching the
> > archives but couldn't find anything - thus, I thought probably I was
> > hallucinating :P
> >
> > So, you want me to revert back the '()' change? Does it impact the expansion
> > of this macro?
> 
> We haven't added this on any other usage of the __extension__ keyword
> in the existing code. From my perspective it is more consistent to
> revert it.
> 
> Anyone else with an opinion here? David? Thomas?

As an exported header, rte_common.h must pass check-includes.sh. Both
typeof() and the ({ ... }) construct are non-standard GCC extensions and
would fail to compile with pedantic options.

-- 
Adrien Mazarguil
6WIND